The present invention relates to a surveying apparatus and method for surveying an object, and in particular, to a surveying apparatus and method for surveying and tracking a moving object.
Optical instruments, such as surveying instruments are commonly used for measuring a position of an object to obtain information, such as horizontal and vertical angles and distance.
A conventional surveying instrument comprises a telescope system for sighting an object which can then be imaged on a camera behind the telescope system. Further, such an instrument may comprise a distance measurement unit to measure a distance to the object sighted by the telescope system. The viewing angle of the telescope system is generally very small, e.g. 1 to 2 degrees, thus also the field of view of the telescope is small and a user has to position the surveying instrument and adjust the optics of the telescope system so that the object to be sighted and to be measured is exactly in the small field of view of the telescope system and optimally on the optical axis of the telescope system, ultimately e.g. to measure a distance to the object.
However, in certain cases the object may move so that the user has to readjust the instrument each time anew before measuring the distance to the object.
Recently, surveying instruments with tracking systems have been proposed to follow the position of a moving object. For example, a laser tracker comprising a laser beam may be used to track an object. Thereby, a pivotable mirror may be used to deflect the focused laser beam in the direction of the object and the direction may then be recorded using the angles of the mirror position, for example for changing the optical axis of the apparatus for distance measurement.
However, tracking an object with the above described instrument is only possible as long the focused laser beam is reflected from a reflector at the object back to the laser tracker. It can be hard to meet this condition, especially when the object is moving quickly.
Therefore, in both of the above described instruments, it is difficult to sight and measure a distance to an object, in particular to an object which is not static with respect to the surveying instrument.
In the first example of the surveying instrument, the user has to adjust the telescope system for each movement of the object, which is time consuming and difficult, especially if the object is not in the small field of view.
In the second example of the surveying instrument, since the tracking is dependent on the laser light hitting a reflector and on the reflected light being received again by the laser tracker, the angles of the laser tracker and of the reflector are crucial.
In addition to the above-mentioned problems, it is also possible that the part of the object carrying the reflector is occluded by an obstacle. This would also render tracking impossible, even so other parts of the object may still be visible.